1. Field of the Invention
The invention relates to an intermittent torque transmission device which is capable of transmitting a greater torque with a relatively simple structure, and particularly is capable of insuring a precise torque transmission without sacrificing its entire compactness so as to comply with the needs of industry.
2. Description of the Prior Art
In modern robotic technology accommodated into various types of industrial machine tools, an index device has been associated with an electric motor in a form of an intermittent torque transmission device. The device intermittently transmits its torque for application to a transfer of robotic arms.
One example of the intermittent torque transmission device is shown in FIG. 9 in which a drive wheel 10 has a groove 20 having cam faces (A), (B) at both walls of the cam groove 20. A driven wheel 30 has cam followers in the form of rollers 40. The rollers 40 are provided at the circumferential periphery of the driven wheel 30. The roller 40 runs along the cam faces (A), (B) in turn in combination with the movement of the drive wheel 10. In this instance, the movement of the driven wheel 30 ceases when the profile of the cam groove 20 is in accordance with the circumferential direction of the drive wheel 10 so as to effect intermittent rotational movement.
However, it has been desirable to improve this type of the intermittent torque transmission device particularly in the following points: (i) With the roller running along the cam faces (A), (B), the transmission torque is borne by a single shaft of the roller, thus making it likely to break the shaft when a greater transmission torque is imposed on the roller. This is also true upon making a compact type of the intermittent torque transmission device. (ii) It is generally difficult to precisely machine the profile of the cam face on which the roller engages. This requires a highly skilled technique and expensive machines to substantially eliminate a backlash play between the roller and the cam face.
In connection with this type of the intermittent torque transmission device, a speed reducer device has been introduced to provide (a) a high reduction ratio with compact structure, (b) a high controlling precision with minimum play of backlash, (c) an elevated rigidity with high meshing rate, (d) an easy controllability improved with a relatively small inertia force, (e) a minimum loss of torque with minimum wear.
This type of the speed reducer device satisfying these advantages (a).about.(e) is shown in U.S. Pat. No. 4,829,851 patented on May 16, 1989 which corresponds to Japanese Patent Application No. 141963/60 filed on Jun. 27, 1985. In this patent, are first and second discs provided each surface of which has a groove defined by a cycloidal-based curve. A plurality of balls are provided to roll along each groove of the first and second discs when a rotational movement is transmitted to the second disc so as to impart the second disc with a nutational movement. A rectifier disc picks up a rotational movement from the nutational movement of the second disc to produce a reduced output.
It is, however, desirable to ensure a greater reduction ratio up to 1/50.about.1/100 in a reducer device particularly employed to machine tools. From the point of strength and machinability, it is thought difficult for the prior reducer to ensure such a great reduction ratio without sacrificing its compactness.
Therefore, it is a main object of the invention to provide an intermittent torque transmission device which is capable of readily machining a cam groove, and achieving a high controlling precision with a minimum play of backlash, a high rigidity with a high meshing degree, an improved controllability with small inertia force and a greater transmission torque with a compact structure.